Control system for engine starters

ABSTRACT

The subject system is designed to control the operation of a gas turbine engine starter. It includes a solenoid valve for governing the flow of operating fluid to the starter motor, an electromagnetic pickup for sensing starter motor speed, a start switch, an overspeed indicator means, and electronic circuit means operative to connect the solenoid with a source of electric current when the start switch is actuated and to disconnect it from the source when the magnetic pickup senses a predetermined speed of the starter motor. The system is operative also to disconnect the solenoid from the current source if a short circuit occurs, or if for any reason the electromagnetic pickup fails to sense motor operation. This disconnecting operation will be repeated each time the start switch is closed until the fault is eliminated. If the solenoid valve fails to close for any reason and the starter motor continues to accelerate, the system operates to energize an overspeed indicator to warn the operator to manually interrupt the starting cycle.

United States Patent Primary Examiner-Robert M. Walker Att0rneys-HersChel C. Omohundro and John N. Hazelwood ABSTRACT: The subject system is designed to control the operation of a gas turbine engine starter. It includes a solenoid valve for governing the flow of operating fluid to the starter motor, an electromagnetic pickup for sensing starter motor speed, a start switch, an overspeed indicator means, and electronic circuit means operative to connect the solenoid with a source of electric current when the start switch is actuated and to disconnect it from the source when the magnetic pickup senses a predetermined speed of the starter motor. The system is operative also to disconnect the solenoid from the current source if a short circuit occurs, or if for any reason the electromagnetic pickup fails to sense motor operation. This disconnecting operation will be repeated each time the start switch is closed until the fault is eliminated. If the solenoid valve fails to close for any reason and the starter motor continues to accelerate, the system operates to energize an overspeed indicator to warn the operator to manually interrupt the starting cycle.

PATEN TEU APR 1 3mm $574,476

SHEET 1 0F 3 INVENTORS. ARTHUR H. JA MET QUINTIN A. JO SON ATTORNEY PATENTED APR13I9YI 34574476 sum 2 or a 25 VALVE SOLENOID SWITCH HOLDING COIL MONOPOLE PICKUP INVENTORS. FIG-2 855%? 268.33%

ATTORNEY PATENTEUAPRIBIBYI 3574476 sum 3 OF 3 ARTHUR $852 35? Fl 2A QUINTIN AjJOHNSON ATTORNEY CONTROL SYSTEM FOR ENGINE STARTERS SUMMARY This invention relates generally to starting apparatus for engines. lt is more particularly related to starting apparatus for engines of the gas-turbine-type wherein the starters have motors which operate at high speed and low torque to start the engines in a relatively short period of time, viz., from just under up to 60 seconds. One of the characteristics of such motors (of which an air turbine is typical) is the rapid acceleration, which, if not closely controlled, may lead to selfdestruction of the motor and possible damage to associated structure, or injury to personnel. More specifically, this invention is directed to an improved control system for starting apparatus of the turbine-motor-operated type, the control system having a magnetic pickup directly responsive to motor speed and an electronic circuit connected with said pickup to be controlled in part thereby.

An object of this invention is to provide an electronic starter control system with which the operator can initiate an enginestarting operation merely by momentarily pressing a start button, after which a sequence of events to complete the start and then inactivate the starter will automatically take place.

Another object of this invention is to provide the starter control system mentioned in the preceding paragraph with means which will automatically abort an engine-starting operation if there is a short circuit in an electrical portion of the system, or if a magnetic speed sensor included in the system becomes inoperative for any reason.

Still another object of the invention is to provide the system of the two preceding paragraphs with means operative, in the event the starter is not automatically inactivated when the engine-starting operation is completed, to give the operator a warning signal that a starter motor overspeed condition is occuring so that he can manually interrupt the starter operation.

A further objectof the invention is to provide a control system for a gas turbine engine starter of the type having an electroresponsive valve for controlling the flow of an operating medium to the starter motor, the control system including a start switch, an electronic circuit means operative to connect the electroresponsive valve with a source of current when the start switch is actuated an electromagnetic pickup disposed adjacent to and responsive to the rotation of the starter motor to apply a signal to the electronic circuit means to disconnect the electroresponsive valve from the current source when the starter motor reaches a predetermined speed, and means connected with the electronic circuit means for energizing a signal to warn the operator in the event the disconnect means malfunctions and the starter motor is caused to overspeed.

A still further object is to construct the electronic circuit means of the control system mentioned in the preceding paragraph with a circuit section which functions automatically to sense the absence of a signal from the electromagnetic pickup for any fault and disconnect the electroresponsive valve from the current source to abort the starting operation, this function being repeated for every start attempted thereafter until the fault is corrected.

Another object is to include a circuit section in the electronic circuit means which senses an overcurrent due to a short circuit and turns off the current, this condition to be maintained until the cause of the short circuit is eliminated.

Other objects and advantages of the invention will be apparent from the following description of one form of the invention illustrated in the accompanying drawings.

THE DRAWINGS FIG. 1 is a schematic of a starter control system embodying the present invention; and

FIGS. 2 and 2A form a diagram of the electronic circuit means utilized in the system shown in FIG. 1.

DESCRIPTION Referring more particularly to FIG. 1 of the drawings, it will be noted that the schematic representation of the starter is designated generally by the numeral 10, and that it will be noted that the schematic representation of the started is designated generally by the numeral 10, and that it includes a turbine wheel 11 on a shaft 12 provided with a pinion 13. The latter meshes with a planetary gear 14 which is connected with a pinion 15 in meshing engagement with an internal ring gear 16. Gear 16 has a ratchet hub 17 for engagement by pawls l8 pivotally carried by a clutch body 20 on an output shaft 21 which may be suitably connected, as by splines 22, with an engine (not shown) or component thereof.

In an engine-starting operation, the turbine wheel 11 is revolved to transmit rotary motion to the engine through shaft 12, pinion l3, gear 14, pinion 15, ring gear 16, ratchet and pawls l7 and 18, respectively, and output shaft 21. The gearing has been designed to convert the high r.p.m. low torque of the turbine wheel into relatively low r.p.m. high torque at the output shaft. The latter is directly connected with the engine and rotates therewith. When the engine r.p.m. equals or starts to exceed the r.p.m. of the ring gear 16, the pawls will be disengaged from the ratchet hub and the starter will cease to transmit torque to the output shaft. To impart rotary movement to the turbine wheel, fluid such as air under pressure is supplied thereto through an inlet duct 23. The turbine depicted is of the centrifugal type in which the motivating fluid is supplied to the central region of the wheel. It will be obvious that turbines of other types, viz., centripetal or axial, could be employed without introducing any change in the invention or sacrificing any of the novelty therein. The flow of fluid through the duct 23 is controlled by a valve 24 which in this example of the invention is shown as a solenoid valve with the field coil designated at 25. When the coil 25 is energized the valve will be opened to apply fluid under pressure to the wheel to effect an engine-starting operation, and when the turbine wheel is rotating at a predetermined speed at which the engine operation will be self-sustaining, the coil will be deenergized to close the valve and terminate the starter operation.

The foregoing construction and operation is substantially conventional, but has been recited here to supply a background for the following description of the control system forming the present invention.

The present invention is directed to a control system for the starter briefly described above. Such control system, designated generally by the numeral 26, includes a start switch 27, an electromagnetic pickup 28 disposed in the form of the invention illustrated adjacent and responsive to rotation of the planetary gear 14, an electronic control box 30, an overspeed indicator 31, and connecting lines collectively designated by the numeral 32. While the electromagnetic pickup 28 is shown as being disposed adjacent and responsive to rotation of the planetary gear, it could without change in principle be positioned near and respond to rotation of the turbine wheel 11. In fact, the pickup is responsive to the rotation of the turbine wheel, although motion is transmitted through shaft 12, pinion 13 and planet gear 14.

The pickup 28 is frequently termed a monopole probe and, as shown in FIG. 2, comprises a core 33 carrying a coil 34 adjacent the planet gear 14. When the turbine wheel revolves, gear 14 will be driven, causing an AC signal to be generated in the coil 34. This signal is transmitted via leads 35 to the electronic control box 30 to effect the interruption of the starting operation when the turbine reaches a predetermined r.p.m. If for any reason the starting operation is not interrupted at the predetermined r.p.m. of the turbine and the latter continues to accelerate, the overspeed indicator 31 will be energized at a predetermined overspeed and the operator will take appropriate action to stop the starting operation.

FIGS. 2 and 2A show a diagram of the solid-state electronic circuit means employed in the control system. The starting switch 27 with its holding solenoid 27A, the field coil 25 of the valve 24, the overspeed indicator 31, the monopole pickup 28, and a suitable current source 36, are also schematically indicated in these figures. As indicated by dot-and-dash lines in FIGS. 2 and 2A, the circuit means in box 30 includes six circuit sections designated by numerals 3742, inclusive. Section 37 is the power supply, 38 the short circuit protection section, 39 the delay section, 40 a frequency detector section, 41 a reference circuit section, and 42 a logic circuit section.

The operation of the system is generally as follows: Starting switch 27 is depressed momentarily to connect the current source 36 with the electronic circuit means ad the field coil 25 of the valve 24. At this time, valve 24 will open to supply fluid under pressure to the turbine to initiate an engine-starting operation. Also, the holding solenoid 27A of the start switch will be energized to hold the switch 27 closed. The starter accelerates, imparting high speed, low torque to the power train 13, 14, 15, and 16, which transmits relatively low speed, high torque through the pawl and ratchet clutch, shaft and spline 22 to the engine. Rotation of the turbine causes the generation of an AC signal in the pickup 28 which is transmitted over leads 35 to the electronic control box 30. When a predetermined speed is reached by the turbine, the electronic control circuit means will deenergize the valve solenoid and the switching-holding solenoid. Switch 27 will then open, valve 24 will close and the turbine will come to a stop.

As pointed out in the objects, one of the aims of this invention is to provide the system with a number of fail-safe features. This objective is partly attained through the inclusion in the power supply section 37 of an input filter consisting of an inductor L1 and capacitor C1 which serve to filter a predetermined transient, Short circuit protection section 38 includes transistors 016 to Q19, inclusive, and associated components connected to operate with a current of about 0.2 amps. Should the current increase to approximately 0.6 amps, transitor Q19 will turn on silicon'controlled rectifier Q18 which turns off the series pass consisting of transistors Q16 and Q17. Diode CR23 clamps inductor L1 when current through transistor 016 is interrupted. Silicon-controlled rectifier 018 will remain turned on until the start switch is pressed, at which time the circuit will reset if the cause of the overcurrent has been eliminated. Reset is accomplished by transistor Q12 which. is turned on by the start switch. The turning on of transistor 012 places a 28-Volt charge on capacitor C20 directly across silicon-controlled rectifier Q18, thereby reverse-biasing it and causing it to turnoff. Diode CR7 clamps the voltage at the base of transistor Q17 to a predetermined voltage,causing transistors Q16 and Q17 to act as emitter followers at higher voltages, thus meeting longterm transient requirements.

The power supply section also includes an inverter composed of transformer Tl transistors 01, Q2, diodes CR3, CR4, CR5, CR6, and associated components which make up a free-running oscillator, using T1 as an auto transformer. Zener diode CR6 clamps or limits the voltage applied to the transformer to a constant 13 Volts. The AC output is a square wave of constant amplitude which is rectified by bridge rectifier CR9 through CR12, the AC output is a square wave of constant amplitude which is rectified by bridge rectifier CR9 through CRl2, the outputs being predetermined positive and negative voltages with respect to ground and filtered by resistor capacitor filters R14C6 and Rl C7. Zener diode CR13 and resistor R16 form a reference voltage circuit to limit and stabilize the output at a predetennined voltage.

Frequency detector section 40 is provided to convert the AC signal generated by the monopole pickup to DC. This section has transitor Q6, transformer T2, transistors Q7 and Q8, resistor R21, capacitors C10, C11 and C12 ad other associated components. The signal from the monopole is changed to a square wave of selected voltage to drive the transformer T2. The output from the latter switches transistors Q7 and Q8 on alternate half-cycles, which in turn switches capacitor C11 alternately in parallel with capacitors C10 and C12. This action results in a voltage across resistor R2] proportional to the frequency of the signal generated by the monopole pickup, which in turn is dependent upon the r.p.m. of the turbine wheel 11.

Reference circuit section 41 has two principal parts comprising integrated circuit amplifiers Al and A2, utilized in this system as comparators. The first is employed as a cutout reference to interrupt starter operation when the turbine wheel has reached a predetermined r.p.m, at which the speed of the engine being started is self-sustaining. Comparator A2 serves an an overspeed reference to effect the energization of the overspeed indicator 31 in the event some failure should occur in the system which would prevent normal interruption of the starting operation. Indicator 31 has been schematically illustrated as a visual signal lamp but could be an audible signalling element or a combination of both if desired. Comparators A1 and A2 with the associated resistors R25 and R30 and capacitors C15 to C19 complete the reference circuit section.

Resistors R26 and R29 are variable and can be set to vary the r.p.m. of the turbine wheel at which the system will function to interrupt the starting operation or give the overspeed warning. When the output voltage from the AC to DC converter reaches and starts to exceed that for which resistor R26 has been set, comparator A1 changes state and drives transistor 010, which causes the system to deenergize the switch-holding solenoid and switch 27 will pop out. The coil 25 of the valve 24 solenoid will also be deenergized, causing the valve to close and interrupt the flow of operating fluid to the starting turbine. The starting operation will then be discontinued. if for any reason the valve should stick open or otherwise fail to close and the turbine should continue to accelerate, the output voltage from the converter will continue to increase. When it reaches and starts to exceed that for which resistor R29 has been previously set, comparator A2 will change state and drive transitor 014 which causes the system to energize overspeed indicator 3]. The operator must then take appropriate action to interrupt the starting operation.

To prevent a starting operation without proper control, a monopole fail-safe circuit means has been provided. This circuit means operates to shut the operating fluid-admission valve in the event the monopole pickup fails for any reason to generate or transmit a signal. This part of the circuit includes the bridge with diodes CRIS through CR18, transistors Q9, Q3, silicon-controlled rectifier Q4, Q5, and associated components. If the monopole pickup is generating a signal transistor O9 is held off. In the absence of such a signal, however, transistor Q9 turns on and the holding coil will be deenergized, assuming transistor O5 is on. Normally, this condition is maintained. To inhibit the fail-safe circuit from shutting off the started before it has accelerated to a speed sufiicient to cause an adequate monopole output, however, a 3-seconds delay circuit, consisting of transistors Q3, Q4 and associated components, is provided. lts operation is triggered by the closure of the start switch. This circuit turns transistor Q5 off for 3 seconds. Thus, if transistor Q9 turns on during the first 3 seconds after the closure of the start switch due to no monopole signal, the interruption will not take place. After the passage of 3 seconds, 05 will be turned on, and if there is still no monopole signal, transistors Q5 and 09 will both be on and the holding coil will be deenergized, permitting the start switch to open. The logic circuit section 42, including transistors O10, O11, O12, O13, Q14, and Q15, working in conjunction with transistors 05 and Q9, implement the time and under what conditions the holding coil should be deenergized to shut down the starter.

As above pointed out, the conditions for starter shutdown are:

l. The attainment of percent of the predetermined turbine speed;

2. The passage of more than 3 seconds after the pressing of the start button and the absence of a monopole signal; and

3. An overcurrent load condition in the indicator or holding coil circuits or within the electronic control box that is capable of drawing more than a predetermined amount of amperage.

To prevent interference with the operation of the system, the lines leading to and from the monopole pickup are shielded as at 43, the shield being connected with a suitable ground.

By way of summary, it may be pointed out that the control system described above serves to start an engine and discontinue the starting operation by automatically stopping the flow of operating medium to the starting motor (turbine) when the latter reaches a predetermined speed of rotation. If for any reason the supply of the operating medium is not interrupted and the motor continues to accelerate, a warning signal will be given at a selected percent in excess of the predetermined speed so that the operator may take appropriate action. The electronic control circuit means has been designed to provide a fail-safe check on the electromagnetic speed sensor or monopole pickup which senses the turbine speed so that the starting operation will be aborted if the pickup fails for any reason to operate or transmit a signal. Other safety features, such as protection against short circuit or overload, are also provided. Since most of the system components, other than the starter, the valve for controlling the air or 1 other operating medium, and the monopole pickup, are connected by electrical lines, they may be disposed at a location remote from the engine, as in the aircraft pilots compartment.

lclaim:

1. In a control system for engine-starting apparatus of the type having a motor, and electroresponsive means for controlling the flow of an operating medium to the motor, the combination comprising:

a. a start switch;

b. circuit means connected with said start switch and operative upon the closing thereof to establish a connection between the electroresponsive means and an electric power source to initiate a flow of operating medium to said motor; and

c. means connected with said circuit and responsive to the operation of said motor to generate a current with a characteristic variable in accordance with the rate of operation of said motor, the characteristic being such that at a predetermined rate of operation of said motor, said circuit means will break the connection between said electroresponsive means and the electric power source and interrupt the flow of operating medium to said motor.

2. A control system according to claim 1 in which the circuit means is of the electronic type and the means responsive to the operation of the motor is an electromagnetic pickup which generates an AC signal with a'frequency proportional to the rate of operation of the motor.

3. A control system according to claim 2 in which the electronic circuit means has a cutout portion operative to break the connection between the electroresponsive means and the electric power source when the electromagnetic pickup produces a signal with a frequency indicative of a predetermined starter motor speed.

4. A control system according to claim 2 in which the electronic circuit means has a monopole check portion operative to break the connection between the electroresponsive means and the electric power source when the electromagnetic pickup fails to produce a signal following the closure of the start switch.

5. A control system according to claim 4 in which the electronic circuit means has a portion which functions to delay the connection-breaking function of the monopole check portion for a predetermined period of time following the closure of the start switch to enable the motor to attain a speed sufficient to cause the electromagnetic pickup to generate a si nal.

6. A con rol system according to claim 2 m WhlCh the electronic circuit means has a short circuit protection portion operative upon the occurrence of an overload to disconnect the current source from the circuit means immediately following the closure of the start switch.

7. A control system according to claim 2 in which the electronic circuit means has aregulator portion operative to prevent transient voltages greater than a predetermined maximum from passing into the other circuit portions.

8. A control system according to claim 2 in which the electronic circuit means has a reference portion including an integrated circuit amplifier with which the signal from the electromagnetic pickup is compared, the reference portion of the circuit being operative when the electromagnetic pickup produces a signal with a frequency indicative of a predetermined starter motor speed to break the connection between the electroresponsive means and the electric power source.

9. A control system according to claim 8 in which the integrated circuit amplifier is adjustable to vary the speed of the starter motor at which the connection between the electroresponsive means and the electric power source will be broken.

10. A control system according to claim 8 in which the reference portion of the electronic circuit means includes a second integrated circuit amplifier with which the signal from the electromagnetic pickup is compared, said second integrated circuit amplifier being operative to energize a warning signal in the event the signal produced by the electromagnetic pickup indicates that the speed of the starter motor exceeds said predetermined rate.

11. A control system according to claim 10 in which a warning signal is provided to be energized when the second integrated circuit amplifier determines that the signal produced by the electromagnetic pickup indicates that the speed of the starter motor exceeds said predetermined rate by a selected percentage thereof.

12. A control system according to claim 10 in which the second integrated circuit amplifier is adjustable to vary the percentage of starter motor speed in excess of said predetermined rate at which said warning signal is energized. 

1. In a control system for engine-starting apparatus of the type having a motor, and electroresponsive means for controlling the flow of an operating medium to the motor, the combination comprising: a. a start switch; b. circuit means connected with said start switch and operative upon the closing thereof to establish a connection between the electroresponsive means and an electric power source to initiate a flow of operating medium to said motor; and c. means connected with said circuit and responsive to the operation of said motor to generate a current with a characteristic variable in accordance with the rate of operation of said motor, the characteristic being such that at a predetermined rate of operation of said motor, said circuit means will break the connection between said electroresponsive means and the electric power source and interrupt the flow of operating medium to said motor.
 2. A control system according to claim 1 in which the circuit means is of the electronic type and the means responsive to the operation of the motor is an electromagnetic pickup which generates an AC signal with a frequency proportional to the rate of operation of the motor.
 3. A control system according to claim 2 in which the electronic circuit means has a cutout portion operative to break the connection between the electroresponsive means and the electric power source when the electromagnetic pickup produces a signal with a frequency indicative of a predetermined starter motor speed.
 4. A control system according to claim 2 in which the electronic circuit means has a monopole check portion operative to break the connection between the electroresponsive means and the electric power source when the electromagnetic pickup fails to produce a signal following the closure of the start switch.
 5. A control system according to claim 4 in which the electronic circuit means has a portion which functions to delay the connection-breaking function of the monopole check portion for a predetermined period of time following the closure of the start switch to enable the motor to attain a speed sufficient to cause the electromagnetic pickup to generate a signal.
 6. A control system according to claim 2 in which the electronic circuit means has a short circuit protection portion operative upon the occurrence of an overload to disconnect the current source from the circuit means immediately following the closure of the start switch.
 7. A control system according to claim 2 in which the electronic circuit means has a regulator portion operative to prevent transient voltages greater than a predetermined maximum from passing into the other circuit portions.
 8. A control system according to claim 2 in which the electronic circuit means has a reference portion including an integrated circuit amplifier with which the signal from the electromagnetic pickup is compared, the reference portion of the circuit being operative when the electromagnetic pickup produces a signal with a frequency indicative of a predetermined starter motor speed to break the connection between the electroresponsive means and the electric power source.
 9. A control system according to claim 8 in which the integrated circuit amplifier is adjustable to vary the speed of the starter motor at which the connection between the electroresponsive means and the electric power source will be broken.
 10. A control system according to claim 8 in which the reference portion of the electronic circuit means includes a second integrated circuit amplifier with which the signal from the electromagnetic pickup is compared, said second integrated circuit amplifier being operative to energize a warning signal in the event the signal produced by the electromagnetic pickup indicates that the speed of the starter motor exceeds said predetermined rate.
 11. A control system according to claim 10 in which a warning signal is provided to be energized whEn the second integrated circuit amplifier determines that the signal produced by the electromagnetic pickup indicates that the speed of the starter motor exceeds said predetermined rate by a selected percentage thereof.
 12. A control system according to claim 10 in which the second integrated circuit amplifier is adjustable to vary the percentage of starter motor speed in excess of said predetermined rate at which said warning signal is energized. 